Toughness is one of the rare intangibles in basketball that is difficult to define in words, and yet most fans know toughness when they see it.

It's a quality that is important to have on your team, especially during the playoffs.

And the kind of toughness I'm talking about is more than just a physical attribute. Mental toughness is even more important.

This list will count down the 15 toughest players left in the playoffs in terms of a combination of both physical and mental toughness.

15: Zaza Pachulia

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Zaza Pachulia is on the list mostly for physical toughness.

He hasn't gotten many minutes the last few years, but his no nonsense, physical defense causes problems for even the league's best centers—just ask Dwight Howard.

14: Kevin Garnett

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In my opinion, Kevin Garnett may be as much of a "fake tough guy" as Chris Bosh, but there's no doubt that scores of NBA fans look at KG and his "intense" attitude as the heart and soul of the Celtics.

Whether or not his antics or game can be seen as "tough" is up for debate, but as a leader of one of the toughest teams in the league, he belongs on the list.

13: Marc Gasol

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Marc Gasol had a fantastic second year in the NBA, but he saw his numbers dip a bit this year.

But in the playoffs, when toughness matters most, Gasol has significantly stepped up his game. His physicality on defense and in the rebounding game has been a crucial part of Memphis's five victories.

12: Tony Allen

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Every successful team needs a little bit of crazy. Tony Allen's brand of crazy helps him to be one of the toughest perimeter defenders in the league.

If the Grizzlies keep this Cinderella run alive (and if Russell Westbrook keeps shooting more than Kevin Durant, they might), Tony Allen is going to cause major headaches for Kobe Bryant or any other wing he might face in the Western Conference Finals.

11: Nick Collison

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On a team that is fairly soft from top to bottom, Nick Collison provides some real toughness inside for the Oklahoma City Thunder.

It takes a mentally tough player to accept the kind of role Collison has. He was a superstar in college but willingly became the "garbage guy" in the pros.

Then, it takes a physically tough player to endure the kind of punishment Collison takes inside while defending opposing bigs who are often significantly bigger and stronger than he is.

10: Josh Smith

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Josh Smith is a physical, athletic forward who can defend two or three different positions.

The verdict is still out on the mental toughness of every member of the Hawks. But we should learn a lot to that end over the course of this Hawks/Bulls series.

If players like Al Horford and Joe Johnson allow themselves to be ignited by the typically tough play of Pachulia and Smith, the Hawks have an outside shot against the Bulls.

9: Joakim Noah

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Much like Kevin Garnett with the Celtics, Joakim Noah can be seen as the "heart and soul" of this team despite not being a major offensive weapon.

Noah plays tough on both ends of the floor, all game long. He plays every defensive possession as if the game depends on it and attacks the glass as aggressively as anyone in the league.

8: Tyson Chandler

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It has become terribly cliche to say that Tyson Chandler has brought toughness to the Mavericks. But in this case, the cliche is true.

I would argue that Chandler over Erick Dampier was the single biggest offseason upgrade of the past year (even more than LeBron James over Dorrell Wright).

Where Dallas once had a bump on a log in the middle of the paint, they now have an aggressive defender, rebounder and finisher inside.

Chandler's intense style and fiery demeanor has rubbed off on a few teammates and helped break the Mavs recent first-round curse.

7: Andrew Bynum

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Yes, I know Andrew Bynum is injury-prone. But you have to give the big man credit for playing through as much pain as he has the last couple years.

You also can't deny the difference between the Lakers with Bynum and the Lakers without him. His toughness inside makes things a lot harder for basket-attacking opponents.

He's been very solid in the playoffs this year, averaging 15 points and 10 rebounds per game.

6: Ron Artest

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If this list was based on physical toughness alone, Artest would easily make the top three. However, while he's much more stable than he used to be, there are still some question marks.

He's nowhere near the perimeter defender he used to be, but his tough brand of defense still frustrates players like Paul Pierce to no end.

5: Zach Randolph

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Zach Randolph has been one of the most underrated players in the league over the last few years. After leading the Grizzlies to a six-game upset of the Spurs and stealing Game 1 from the Thunder, people are taking notice of Randolph.

Talent is a huge part of his game, but his toughness is essential as well. That attribute helped him finish third in the league in rebounding and second in offensive rebounding this past season.

4: Rajon Rondo

A big sign of toughness is the way a player performs in the postseason. Rondo has put up solid regular season numbers the last couple years, but he steps up his game significantly in the playoffs.

His averages for points, rebounds and assists are all much better in the postseason than they are in the regular season.

His tough style has been a big part of Boston's success since they assembled "The Big Three."

3: Derrick Rose

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Derrick Rose's mental toughness is particularly impressive when you consider his age and experience. At just 22 years old and in his third season, Rose has already displayed the kind of "killer instinct" required to win a championship.

As much as anyone in the league, Rose possesses a "can't lose" attitude.

Then there's the physical side of his toughness. He's 6'3" and under 200 lbs but fearlessly attacks the rim and all defenders in his path in a way that's hard to describe.

2: Dwyane Wade

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Dwyane Wade is the only player on the Heat who meets the requirements for this list. That's what worries me about Miami's chances to win a title.

Of course, one tough guy is better than none, and in terms of physical and mental toughness, it doesn't get much better than Wade.

He has no fear when he attacks the basket, he's played through plenty of pain, has the killer instinct and already has an NBA title on his resume. His toughness is central to all of that.

1: Kobe Bryant

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There may not be a player in the league with more mental toughness than Kobe Bryant.

Over the last two-and-a-half years, no one has demonstrated the "will to win," "killer instinct," etc as much as Kobe has.

He's given his team more big shots and big performances in big moments than any other player in the NBA has done for their teams.

He's had to deal with a hatred from opposing fans that no other player (with the possible exception of LeBron) can possibly understand.

He has to deal with every team's best or most frustrating perimeter defender, is punished by big men when he goes inside and gets fewer "superstar calls" than any other superstar.

Even with all that, Kobe continues to show his mental toughness by rising above and winning.

Don't forget the fact that he's played through several nagging injuries over the last few years. Physical toughness? Yeah, he's got that too.